2. Objective C
• Objective C is a programming language, which is used by Apple for
developing the application for iPhone and Mac Systems.
• Objective C is very old programming language and it was designed and
developed in 1986. Now Objective C has become popular once again as it is
being used by Apple to develop applications for Mac system and iPhone.
• Full superset of C language
• Allows any traditional C code.
• Adds powerful Object oriented capabilities.
3. OverView
• Objective C consists of objects, classes, instance variables,
methods.
• Built entirely around objects.
• Objects like Windows, views, buttons, controllers exchange
information with each other, respond to events, pass actions to run a
program.
• In C we write .c and .h files, here we write .h and .m files.
• .h are the header files and .m are the source code or implementation
files.
5. Keywords
Keywords in objective C has a prefix @ appended to them. We will look at the
keywords used for different purposes in this section
Keyword
Definition
@interface
This is used to declare a class/interface
@implementation
This is used to define class/category
@protocol
This is used to declare a protocol
6. Keywords Cont…
Interface
The declaration of a class interface begins with the compiler directive
@interface and ends with the directive @end.
@interface ClassName : ItsSuperclass
{
instance variable declarations
}
method declarations
@end
the name of the interface file usually has the .h extension typical of header
files.
7. Keywords Cont…
Implementation
The definition of a class is structured very much like its declaration. It
begins with the @implementation directive and ends with the @end directive
@implementation ClassName : ItsSuperclass
method definitions
@end
The name of the implementation file has the .m extension, indicating that it
contains Objective-C source code.
8. Keywords cont..
Next are the access modifiers. They decide the visibility/ scope of the instance
variables/methods
Keyword
Definition
@private
The instance variable is accessible only within the class that declares it.
@public
The instance variable is accessible everywhere
@protected
The instance variable is accessible within the class that declares it and within
classes that inherit it.
9. Keywords Cont…
Other keywords:
Keyword
Description
@class
Declares the names of classes
defined elsewhere.
@”string”
Defines a constant NSString object
in the current module and initializes
the object with the specified string.
@property
Provides additional information
about how the accessor methods
are implemented
@synthesize
Tells the compiler to create the
access or method(s)
10. Keywords Cont…
Declaring a simple property
@interface MyClass : NSObject {
float value;
}
@property float value;
@end
A property declaration is equivalent to declaring two accessor methods i.e.
-(float)value;
-(void)setValue:(float)newValue;
These methods are not shown in the code but can be overridden.
11. Keywords Cont…
Synthesizing a property with @synthesize
@implementation MyClass : NSObject
@synthesize value;
@end
When a property is synthesized two accessor methods are generated
i.e.
-(float)value;
-(void)setValue:(float)newValue;
These methods are not shown in the code but they can be overridden.
12. Keywords Cont…
Self
l
Self is a keyword which refers to current class.
{
[self setOrigin:someX :someY];
}
In the example above, it would begin with the class of the object receiving
the reposition message.
13. Keywords Cont…
super
l
l
It begins in the superclass of the class that defines the method where
super appears.
Super is a keyword which refers to the parent class.
{
[super init];
}
{
[super dealloc];
}
In the example above, it would begin with the superclass of the class
where reposition is defined.
14. Message
• It’s the most important extension to C
• Message is sent when one object asks another to perform a specific action.
• Equivalent to procedural call in C
• Simple message call looks like [receiver action], here we are asking the
.
receiver to perform the action
• Receiver can be a object or any expression that evaluates to an object.
• Action is the name of the method + any arguments passed to it.
15. Message with Arguments
• Sometimes we pass one or more arguments along with the action to the
receiver.
• We add a argument by adding a colon and the argument after the action like
[receiver action: argument]
• Real world example of this is [label setText:@”This is my button”];
• String in Objective C is defined as @””;
• Multiple arguments can be passed to a action like this
[receiver withAction1:argument1 withacction2:argument2];
For example:
[button setTitle:@”OK” forState:NO];
16. Classes and Method Declaration
• Class in objective C is a combination of two files ie .h and .m
• .h file contains the interface of the class.
• .m contains the implementation
Class Definition
.h file
.m file
@interface
@implementation
Variable and methods
declaration
Method definitions
17. Classes and Method Declaration
• Example of a Person class.
• Here we define the interface and implementation in Person.h and Person.m
file respectively
Person.h file
#import<Foundation/NSObject.h>
@interface Person: NSObject
{
NSString *name;
}
-(void) setName: (NSString *)str;
+(void) printCompanyName;
@end
18. Classes and Method Declaration
•
Now the contents of Person.m file
•
#import Person.h
@implementation Person
-(void) setName: (NSString *) str
{
name=str;
}
+(void) printCompanyName
{
printf(“This is class method”);
}
@end;
Here we have defined a Class Person which has a instance variable “name” and
a method “setName”.
19. Classes and Method Declaration
• Using the Person class
#import<stdio.h>
#import “Person.m"
int main()
{
Person *c = [[Person alloc] init]; // Allocating and initializing Person
[c setName : @”Rahul”]; // Setting Name of the allocated person
[Person printCompanyName] // calls class method
[c release]; // releasing the person object created
return 1; // return
}
20. Instance and Class Methods
• In objective C we can define methods at two levels ie Class Level and
Instance level
• In previous Example we declared a method with a – sign prefixed. That was
a instance level method.
• If we put + instead of – then we get a class level method.
• A instance method can be called by the instances of the class. But a class
level can be called without creating any instance.
• Example to call a instance method;
Person *p=[[Person alloc] init];
[p setName:@”Sunil”];
• Example to call class method
[Person printCompanyName];
21. Creating multi parameter method
Objective-C enables programmer to use method with multiple
parameter. These parameter can be of same type or of different
type.
MyClass.h
MyClass.m
#import<Foundation/NSObject.h>
#import<stdio.h>
#import"MyClass.h"
@interface MyClass:NSObject{
}
// declare method for more than one
parameter
-(int) sum: (int) a andb: (int) b andc:
(int)c;
@end
@implementation MyClass
-(int) sum: (int) a andb: (int) b andc:
(int)c;{
return a+b+c;
}
@end
22. Creating multi parameter method
Objective-C enables programmer to use method with multiple
parameter. These parameter can be of same type or of different
type.
main.m
#import"MyClass.m"
int main()
{
MyClass *class = [[MyClass alloc]init];
NSLog(@"Sum is : %d",[class sum : 5 andb : 6 andc:10]);
[class release];
return ;
}
Output:
Sum is: 21
23. Constructors
• When a class is instantiated a constructor is called which is used to initialize
the object properties
• When a constructor is called it returns an object of a class.
• If a user does not provide a constructor for a class the default one is used.
• The default constructor is
-(id) init;
id is a special keyword in Objective C which can be used to refer to any
object.
• Remember in our Person class example while instantiating the Person class
we called the constructor.
[[Person alloc] init];
It returns a person object.
24. Categories
• Typically when a programmer wants to extend the functionality of a
class, he subclasses it and adds methods to it.
• Categories can be used to add method to a class without
subclassing.
• Here’s how you create a category
@interface PersonCategory (personcat)
@implementation PersonCategory (personcat)
25. Categories
•
•
•
Implementation of category.
personcat.h file contains
#import “Person.h"
@interface Person (personcat)
-(void) updateName: (NSString *) str;
@end
personcat.m file contains
#import “personcat.h ”
@implementation Person (personcat)
-(void) updateName: (int)value{
Printf(“%d”,value);
}
@end
The updateName name method now behaves as if it’s the part of Person Class.
26. Protocols
• Protocols are like interfaces in Java
• It declares a set of methods, listing their arguments and return types
• Now a class can state that its using a protocol in @interface statements in .h
file
• For example
@interface Person:NSObject <human>
Here human is a protocol.
• Defining a protocol
@protocol human <NSObject>
-(void) eat;
@end
27. Keywords Cont…
• Memory management keywords
Keyword
Description
Alloc
Allocates memory for an object
Retain
Retains a object
Releae
Releases memory of an object
Auto release
Auto release memory used by an object
28. Memory Management
• In objective C a programmer has to manage memory ie allocate and
deallocate memory for objects.
• While instantiating a person object we allocated the memory for the object
by this call.
Person *p=[[Person alloc] init];
• We have to release whatever objects we create programatically. Memory
management for other objects is taken care of by the Objective C runtime.
• We use release action to release the unused memory.
The syntax for this is [p release];
